Process of blow molding hollow articles



Nov. 29, 1966 w. H. WEST PROCESS OF BLOW MOLDING HOLLOW ARTICLES 5Sheets-$heet 1 Filed Nov. 13, 1963 Nov. 29, 1966 w. H. WEST 8,288,898

PROCESS OF BLOW MOLDING HOLLOW ARTICLES Filed Nov. 13, 1963 5Shee1zs-$heet 2 Nov. 29, 1966 w. H. WEST PROCESS OF BLOW MOLDING HOLLOWARTICLES 5 Sheets-Sheet 5 Filed Nov. 13, 1963 Nov. 29, 1966 W. H. WESTPROCESS OF BLOW MOLDING HOLLOW ARTICLES Filed Nov. 13, 1963 r/ZZ (/30 5Sheets$heet 4 United States Patent ce 3,288,898 PROCESS OF BLOW MOLDINGHOLLOW ARTICLES Walter H. West, Bay City, Mich., assignor to The DowChemical Company, Midland, Mich., a corporation of Delaware Filed Nov.13, 1963, Ser. No. 323,406 7 Claims. (Cl. 26498) This invention relatesto a novel blow molding method and apparatus and more particularly to amethod and an apparatus for blow molding hollow articles, such asbottles, jars, doll heads and bodies, and the like of thermoplasticwhereby multidirectional orientation is imparted to the molecules ofsaid thermoplastic for multidirectional strength.

In conventional blow molding techniques for forming hollow articles ofplastic, a relatively thickwalled tube is first extruded. Then the tube,or parison, as it is termed in the trade, is clamped at both ends withina mold whose cavity conforms to the article to be blown. It is thenheated and blown until it conforms to the mold walls. Y

Variations on this technique exist but in each instance there is sometechnological difficulty. For example, the

technique which requires the separate forming of a cupshaped parisonprior to blowing increases the processing steps and time, and the amountof molding equipment needed. The technique which requires reheating ofthe parison prior to blowing necessitates additional heat and closetemperature control. Where the technique involves clamping, a flash-trimoperation is frequently needed to provide an attractive finishedarticle. Overriding all of these technological difiiculties is the problem of imparting multidirectional strength to the molded article.Unfortunately, blow molding does not impart sufiicient orientation tothe molecules of the thermoplastic being used. The blown article is weakin the hoop direction so that vertical cracking frequently occurs duringuse of the article. An object of this invention is to provide a novelblow molding technique and apparatus therefor.

Another object of this invention is to provide a blow molding techniquewhich imparts a multiaxial orientation to the blown article. i j

Still another object is to provide a blow molding technique which isoperative at milder temperature condi- -tions.

Another object is to providea blow molding technique which is fast.

Another object is to provide apparatus in a blow mold in which extrusionas well as blow molding can be performed.

Another object is to provide blow mold apparatus which automaticallyimparts multiaxial orientation to the finished article.

Another object is to provide blow mold apparatus which is relativelysimple in structure.

Another object is to provide a blow mold apparatus which does not havelong flow areas to deleteriously atfect the flow.

3,288,893 Patented Nov. 29, 1966 Another object is to provide blow moldapparatus which operates under relatively cold temperature conditions.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others and theapparatus embodying features of construction, combination of elementsand arrangement of parts which are adapted to effect such steps, all asexemplified in the following detailed disclosure, and the scope of theinvention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIGS. 1 through 4 are cross-sectional schematic views of one embodimentof apparatus for blow molding a plastic bottle arranged to show thesequential order of operation.

FIGS. 5 through 8 are cross-sectional schematic views of anotherembodiment of the blow mold apparatus similarly arranged to show thesequential order of operation.

FIGS. 9 through 12 are cross-sectional schematic views of still anotherembodiment of the blow mold apparatus.

FIGS. 13 through 16 are cross-sectional schematic views of anotherembodiment of the blow mold apparatus, and

FIGS. 17 through 20 are cross-sectional schematic views of anotherembodiment of the blow mold apparatus.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

As seen in the several sets of schematic views of the drawings, it hasbeen found that an improved blow molded plastic article can be producedby extruding plastic through an annular die orifice, one lip of which isrotating with a level of torque sufiicient to impart molecularorientation to the extruded plastic, and immediately blowing theextruded plastic out to conform to the surrounding walls of the blowmold cavity.

More particularly, it has been found that exceptional strength isimparted to a blow molded article by causing molecular orientation ofthe plastic prior to blowing. This is accomplished by extruding the rawplastic through an annular die orifice 1 in the drawings'whileone-element of said orifice is being rotated with a levelof torquesufficient to impart orientation to the molecules of the plastic beingextruded. As soon as the plastic leaves the extrusion orifice, it isblown into the shape defined by the cavity of the mold, a bottle mold 2in the drawings, which surrounds the orifice. There is no solidificationof the plastic between the extrusion and the blowing step so that inessence a singular extrusionblowing process occurs. This permits use ofraw plastic in a solid, granular or fluid form. The several embodimentsshown in the drawings illustrate each such use.

The apparatus illustrated in FIGS. 1 through 4 permits use of a solidrod-like parison preferably in a heated state. It consists of a bottlemold 2 which in this instance consists of a left and a right moldelement 10 and 12, respectively, parting on a center line (not shown)and having a threaded neck portion 14 within the entrance port 16 of thecavity when the elements are in abutting relationship. A solid rod 18 ofthermoplastic material in this instance can be used as the parison. Itis inserted through port 16 into the cavity of parison cylinder 20.Cylinder 20 is reciprocally mounted within bottle mold 2 through lowerparison cylinder port 22 within mold 2. Plug 24 within parison cylinder20 acts as a floor suporifice 1 retains its original annular dimension.

cavity of the bottle mold 2.

to insertion into the parison cylinder 20, it extrudes the parisonoutwardly as illustrated in FIG. 2, so that the upper level of theparison expands against the threaded neck section 14 of the bottle mold2 and then the balance of the parison is extruded outwardly through anannular die orifice 1, formed between the plunger 28 and the upper edgeof parison cylinder 20.

At the same time compressed air or gas is forced into the cavity 30 ofthe mold via air passageway 32 within plunger 28 to blow the extrudedportion of the parison outwardly. Simultaneous with downward movement ofthe blow plunger 28, the parison cylinder also travels downwardly at thesame relative speed so that the die Also, during movement of the blowplunger 28, it is rotated with a level of torque sufficient to impartorientation to the molecules of the plastic being extruded. The outwardblowing of the extruded portion of the parison, as the rotating plungertravels downwardly, further causes longitudinal strain upon themolecules with the net result that a fully oriented blown bottle 34having multiaxial orientation is produced.

Downward movement of the blow plunger 28 and the parison cylinder 20terminates when both reach the bottom of the bottle mold, as seen inFIG. 4. As shown, a

disk-shaped concave depression will be formed in the bottle.

If other configurations are used for the die orifice, a flat bottomedbottle, a round concave bottomed bottle or other bottom shapes will beproduced. Anyway, at this point, the blown bottle is fully formed and byretracting the blow plunger 28 and opening the bottle mold 2, thefinished bottle can be removed.

The bottle so formed has multiaxial orientation in the longitudinal andlatitudinal directions so that it has great strength. In addition,trimming of the neck, body or bottom of the bottle is avoided due to themethod of forming utilized.

FIGS. 5 through 8 illustrate a variation of the method utilized in FIGS.1 through 4. Instead of a solid rodlike parison, the apparatus shownpermits use of a liquid parison which is extruded directly into the blowmold In this embodiment, the bottle mold consists of reciprocal cylinder50 of inverted cup-shaped configuration. If desired, it can be formed oftwo half round shells to facilitate removal of the finished bottle.

Within the cylinder 50 is a stationary parison cylinder 52 which alsoacts as a bottle mold piston. Within the center of the parison cylinder52 is a parison cavity 54 into which molten plastic 56 is first extrudedfrom extruder 58. After such extrusion, parison piston 60 advances theparison 56, in molten form, to an annular die orifice 1 which, in thisembodiment, is formed between parison cylinder 52 and blow plunger 62.This causes extrusion of the molten plastic out through the orifice 1into bottle mold cavity 66. As such extrusion occurs,

compressed air or gas is supplied via air passageway 68 in plunger 62 tothe center of the orifice extruded parison where the air or gas blowsthe plastic outwardly to eventually conform to the Walls of the bottlemold ficient to impart multiaxial orientation to the molecules of theplastic being blown into bottle shape.

It should be evident that dependent upon the length of upward stroke ofthe bottle mold cylinder 50, various height bottles can be formed. Thus,by appropriate setting of the vertical stroke of the bottle moldcylinder 50, one can automatically produce different sized bottles. Dueto formation of the bottle neck as shown, there is no trim problem.Also, unique multidirect-ional strength has been imparted to the formedbottle by rotating the blow plunger 62 during extrusion. It is alsoconceivable to construct the apparatus shown to provide for rotation ofthe parison cylinder 52 instead of the blow plunger whereby a likeorientation of the molecules of the plastic will be effected.

FIGS. 9 through 12 illustrate still another variation of method andapparatus, particularly with respect to the apparatus shown in FIGS. 5to 8. Like the method illustrated in FIGS. 5 to 8, it too involves theuse of a molten parison.

The apparatus consists of the usual bottle mold 2, but here it takes theform of a cup-shaped cylinder within which bottle mold piston 92reciprocates.

A molten parison 94 is first extruded via extruder 96 into the cavity ofa parison cylinder 110. Then parison piston 98 extrudes the parison intothe bottle mold cavity, as in the apparatus described above. Here again,the extruded plastic first conforms to the bottle thread section 100within the bottle mold piston 92 (FIG. 10). Then, as the balance of theparison is extruded through die orifice 1 (see FIG. 11), the bottle moldpiston 92 travels upwardly. During such movement, the blow plunger 102supplies air under pressure, via air passageway 104, to the moltenparison to blow into a bottle 106 whose shape conforms to the moldcavity 108 (see FIG. 12). Again, at all times, the clearance between theblow plunger 102 and parison cylinder 110 is maintained uniformly toprovide a uniform annular orifice 1. In addition, the blow plunger iscontinuously rotated with a specific level of torque sufiicient toprovide a strain upon the molecules of the molten plastic to impartmultidirectional orientation thereto.

A trimless plastic bottle with multidirectional strength is formed usingthe above apparatus and process.

With the arrangement shown in FIGS. 9 through 12, it is also possible,as in FIGS. 5 to 8, to form bottles of various heights, dependent uponthe range of travel of the bottle mold piston 92, and by the height ofbottle mold cylinder 90.

FIGS. 13 through 16 illustrate still another embodiment of the apparatusand method. Here, a powdered or granulated polymer raw material isutilized to form the parison which is subsequently extruded to form thebottle by blow molding the extrudate.

As illustrated, the apparatus consists of a blow mold 2 with acup-shaped cylinder and bottle mold piston 132 within its cavity. Thepiston contains a parison forming cavity 134 within its axial region.The lower end of the cavity has a threaded neck section 136 for thebottle to be blown.

Granulated polymer 138 is first poured into the cavity 134. Then theblow plunger 140 first descends with great pressure to impact mold thegranulated polymer into a cup-shaped parison 142 (see FIG. 14). Suchimpact molding causes the polymer of the parison to have a fluidlikeconsistency.

Now, after formation of the parison 142, bottle mold piston 132 and blowplunger 140 move upwardly (compare FIGS. 15 and 16), however, the blowplunger 140 moves upwardly at a slower rate, so that successiveextrusion of the fluid parison occurs during such upward movement. Atthe same time, air or gas, in a compressed state, is forced into thecavity of the parison via air passageway 144 to cause expansion of theextrudate to conform to the bottle mold cavity. In this instance, thedie orifice 1 is the clearance between the lower portion of blow plunger140 and the walls of parison forming cavity 134.

Here also, the blow plunger is continuously rotated during the bottleforming operation with a level of torque sufiicient to place a strainupon the molecules of the plastic being extruded. Such strain imparts amultidirectional orientation to the molecules and hence amultidirectional strong bottle 146 is formed.

It should be evident from the illustration in FIGS. 13 through 16, thatthe apparatus could be used to form different height bottles. In suchinstance, the bottle mold 130 must be of suflicient height and thepiston 132 must have sutlicient reciprocal motion to provide for suchvariation in bottles. Thus, by merely varying the stroke of the piston132 between production lots, one can produce bottles of various sizes.

FIGS. 17 through 20 illustrate still another method and apparatus. Here,granulated polymer may likewise be utilized. Or else a solid cup-shapedparison may be used.

To commence the making of bottles, the operator or the apparatus poursgranulated polymer 170 into the neck forming cavity 172 of blow mold 2.The floor of the cavity 172 consists of a parison support piston 174.After a proper amount of raw plastic is fed into cavity 172, blowplunger 176 travels downwardly and compresses the granulated polymerinto a parison 178 (FIG. 18). Then both the blow plunger 176 and theparison support piston 174 travel downwardly with the same relativespeed until the bottom of the bottle is reached. During such movement,the parison is extruded into the bottle mold cavity 180 and blown withcompressed air or gas from air passageway 179 to cause the extrudate toeventually conform to the internal surface of cavity 180 of the bottlemold 2. Simultaneous therewith, the blow plunger rotates with a level oftorque to cause orientation of the molecules of the plastic beingextruded. As above, a strong flash-free bottle is formed.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efiiciently attained and,since certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention, which as amatter of language, might be said to fall therebetween.

Now that the invention has been described, what I claim as new anddesire to secure by Letters Patent is:

1. A method for blow molding hollow thermoplastic articles wherebymultidirectional orientation is imparted to the molecules of saidthermoplastic for multidirectional strength comprising placing a body ofthermoplastic out of which said article is to be formed within 'a cavityhaving an open end within a blow mold, forcing a blow plunger againstsaid body of thermoplastic,

progressively extruding a portion of said parison through an annular dieorifice while rotating at least one lip element of said orifice with atorque sufiicient to impart multidirectional orientation to themolecules of the thermoplastic being extruded.

and blowing said extruded portion outwardly to conform to the walls ofsaid blow mold,

whereby a blow molded object of multidirectional strength will beformed.

2. A method for blow molding hollow thermoplastic articles wherebymultidirectional orientation is imparted to the molecules of saidthermoplastic for multidirectional strength comprising confining a solidrod-like parison within a cavity hav-.

ing an open-end within a blow mold,

forcing a blow plunger against said parison to cause progressiveextrusion of said parison out of the open end of said cavity whilerotating said blow plunger with a torque sutficient to impartmultidirectional orientation to the molecules of the thermoplastic beingextruded,

and blowing said extruded portion outwardly to conform to the walls ofsaid blow mold,

whereby a blow molded object of multidirectional strength will beformed.

3. A method for blow molding hollow thermoplastic articles wherebymultidirectional orientation is imparted to the molecules of saidthermoplastic for multidirectional strength comprising confininggranular thermoplastic out of which said article is to be formed withina cavity having an open end within a blow mold, forcing a blow plungeragainst said granular thermoplastic to cause impact molding into aparison,

progressively extruding said parison out of the open end of said cavityby means of said blow plunger while rotating said blow plunger with atorque sufficient to impart multidirectional orientation to themolecules of the thermoplastic being extruded,

and blowing the extruded portion outwardly to conform to the walls ofsaid blow mold,

whereby a blow molded object of multidirectional strength will beformed.

4. A method for blow molding hollow thermoplastic articles wherebymultidirectional orientation is imparted to the molecules of saidthermoplastic for multidirectional strength comprising confininggranular thermoplastic out of which said article is to be formed withina cavity having an open end within a blow mold, forcing a blow plungeragainst said granular thermoplastic to cause impact molding into aparison, positioning a support against said impact molder parison atsaid open end,

progressively extruding said parison out of the open end of said cavityby means of said blow plunger while rotating said blow plunger with atorque sufiicient to impart multidirectional orientation to themolecules of the thermoplastic being extruded,

and blowing the extruded portion outwardly to conform to the walls ofsaid blow mold,

whereby a blow molded object of multidirectional strength will beformed.

5. Apparatus for blow molding hollow thermoplastic articles ofmultidirectional strength comprising;

a blow mold with a cavity therein,

means for confining raw thermoplastic, said means opening into thecavity of said blow mold and comprising a hollow tubular parisoncylinder which is reciprocally mounted within said cavity,

blow means which partially block opening of said parison cylinder, saidblow means being reciprocally mounted within said cavity whereby anannular die orifice is continuously eifected between said parisoncylinder and said blow means as said elements reciprocate within saidblow mold cavity,

rotating means operatively connected to said blow means for rotatingsaid blow means with a torque sufiicient to impart multidirectionalorientation to the molecules of said thermoplastic,

extrusion means to extrude said thermoplastic out through said annulardie orifice into said blow mold while said blow means are being rotatedand supply means for said blow means to blow said thermoplastic, as itis extruded, to conform to said cavity of said blow mold,

whereby a hollow thermoplastic article of multidirectional strength canbe produced.

6. Apparatus for blow molding hollow thermoplastic a blow mold formed ofa cup-shaped cylinder and a reciprocal piston therein and defining avariable cavity acting as a parison cavity,

a parison support piston reciprocally mounted within 40 blow plungermeans capable of entering and reciprocally moving within said parisoncavity to act as an impact mold plunger to form a parison and as anextrusion plunger to extrude the formed parison, the

blow mold cavity therebetween, lower portion of said blow plunger beingspaced a parison cavity axially located within said piston and from theWalls of said parison cavity whereby a opening into said blow moldcavity only when said uniform annular die orifice may be effectedbetween piston is spaced from the bottom of said cup-shaped said wallsand said lower portion of said blow cylinder, plunger, blow plunger me ncapable of entering d ecip- 10 rotating means operatively connected tosaid blow rocally moving within said parison cavity to act as plungermeans with a torque sufficient to impart an impact mo1d plunger to f aparison d as multidirectional orientation to the molecules of said anextrusion plunger to extrude the formed parison, e mop stic, to lowerportion of said blow plunger being spaced impact d force pply ng meansfor said plunger from the walls of said parison cavity whereby a wherebyraw granulated thermoplastic within said uniform annular die orifice maybe elfected between parison Cavity y be formed into a parison, saidwalls and said lower portion of said blow extrusion forceapplying-meamfor said plunger whereplunger, by said parison may be successivelyextruded out rotating ean operatively connected t id bl through saidannular die orifice into said blow mold plunger means for rotating saidblow plunger means cavity While Said Plunger means are bfiing IOtatedwith a torque suflicient to impart multidirectional and orientation tothe molecules of said thermoplastic, Supply mfians for Said blow Plungermeans t0 blow Said impact mom force applying means f id phmger extrudedparison to conform to said cavity of said whereby raw granulatedthermoplastic within said blow mold, parison it may b f d i a parison,and said reciprocating means for said parison support extrusion forceapplying means for said plunger Piston having means to feciProcate SaidPiston y whereby said parison may be successively extruded fmm Saidextruded and blow p out through said annular die orifice into said blowmold cavity while said plunger means are being References Cited by theExaminer rotated and UNITED STATES PATENTS pply means f r a l plungmeans to blow 2,706,308 4/1955 Lorenz 264 97 2:3 gff f fg to conform of3,059,277 10/1962 Pierce et a1 18 14 whereby a hollow thermoplasticarticle of multidirecr 3109198 11/1963 Gmgnard 18 30 X tional strengthcan be produced. FOREIGN PATENTS 7. Apparatus for blow molding hollowthermoplastm articles of multidirectional strength comprising: 223 2 ablow mold with a cavity thereln, a portion of said 703,970 2/1954 GreatBritain.

ROBERT F. WHITE, Primary Examiner. I. A. FINLAYSON, Assistant Examiner.

said blow mold and capable of providing a floor support to said parisoncavity, means to reciprocate said parison support piston,

1. A METHOD FOR BLOW MOLDING HOLLOW THERMOPLASTIC ARTICLES WHEREBYMULTIDIRECTIONAL ORIENTATION IS IMPARTED TO THE MOLECULES OF SAIDTHERMOPLASTIC FOR MULTIDIRECTIONAL STRENGTH COMPRISING PLACING A BODY OFTHERMOPLASTIC OUT OF WHICH SAID ARTICLES IS TO FORMED WITHIN A CAVITYHAVING AN OPEN END WITHIN A BLOW MOLD, FORCING A BLOW PLUNGER AGAINSTSAID BODY OF THERMOPLASTIC, PROGRESSIVELY EXTRUDING A PORTION OF SAIDPARISON THROUGH AN ANNULAR DIE ORIFICE WHILE ROTATING AT LEAST ONE LIPELEMENT OF SAID ORIFICE WITH A TORQUE SUFFICIENT TO IMPARTMULTIDIRECTIONAL ORIENTATION TO THE MOLECULES OF THE THERMOPLASTIC BEINGEXTRUDED. AND BLOWING SAID EXTRUDED PORTION OUTWARDLY TO CONFORM TO THEWALLS OF SAID BLOW MOLD, WHEREBY A BLOW MOLDED OBJECT OFMULTIDIRECTIONAL STRENGTH WILL BE FORMED.